In a medical filed, nuclear medical diagnosis equipment is used, in which radiations (example, γ rays) emitted from radiopharmaceuticals administered to a subject and localized at regions of interest are detected and a tomographic image of a radiopharmaceutical distribution in the regions of interest of the subject is obtained. As popular nuclear medical diagnosis equipment, a PET (Positron Emission Tomography) device, a SPECT (Single Photon Emission Computed Tomography) device, etc., are known. In such nuclear medical diagnosis equipment, three-dimensional volume data showing a concentration distribution of radioactive pharmaceuticals is reconfigured using radiation detection data. Then, the equipment displays a tomographic image at a predetermined slice cross-section based on the three-dimensional volume data, so that a diagnosis is performed.
As a display method for overviewing an entire tomographic image obtained by conventional nuclear medical diagnosis equipment, a maximum intensity projection method (MIP: Maximum Intensity Projection) is widely used. A maximum intensity projection image (MIP image) projected by the MIP is an image in which the maximum pixel value in the projection path is set as a luminance value at the time of projecting an object. A plurality of MIP images projected in a plurality of directions in which a predetermined direction is set as a central axis are generated, and using a tomographic image display device, these plural MIP images are displayed like, for example, a rotating moving image (see, e.g., Patent Document 1). Hereinafter, the predetermined direction which becomes a central axis at the time of generating a series of MIP images is denoted as “MIP-axis”.
When generating a series of MIP images, as shown in FIG. 14A, with respect to three-dimensional volume data of a region of interest R, for example, an MIP image A1 is acquired in a projection direction S1 parallel to the x-direction, and an MIP image A2 is acquired in a projection direction S2 parallel to the y-direction. By referring to the MIP image A1 and the MIP image A2 acquired in different projection directions, an operator can intuitively know the approximate position P of the region in which radioactive pharmaceuticals are integrated in the region of interest R.
As described above, the image display method by the MIP is very useful for confirming the approximate information before scrutiny diagnosing the tomographic image. In FIG. 14A, MIP images are generated in a manner such that the axis S3 which passes through the center point of the region of interest R and is parallel to the z-axis is set as an MIP-axis.
In nuclear medicine diagnoses, as shown in FIG. 14B, in cases where a region of interest is a whole-body of a subject M or within a range R1 on the median line, a series of MIP images are generated in a manner such that the median line L1 of the subject M is set as an MIP-axis. On the other hand, in cases where a region of interest is a shoulder portion shown by the symbol R2 or the like, there is a case in which the median line L1 falls outside the range of the region of interest.
Under the circumstance, conventionally, a method (Sliding Thin Slab MIP method; hereinafter abbreviated as “Sliding method”) is used, in which a series of MIP images are generated while moving the MIP-axis toward the center line of a region of interest in accordance with the movement of the region of interest (see, e.g., Non-Patent Document 1). In the sliding method, when the region of interest is within a range R2, the projection of the MIP image is performed by moving the MIP-axis from the median line L1 to the center line L2 of the range R2. By such a method, with respect to a local region away from the median line, a series of MIP images with less blur of each projection position can be acquired.